Editing Molecular orbital theory (section)

{{Short description|Method for describing the electronic structure of molecules using quantum mechanics}}
{{See also|Molecular orbital}}
{{Use American English|date=February 2019}}
{{Electronic structure methods}}

In [[chemistry]], '''molecular orbital theory''' (MO theory or MOT) is a method for describing the electronic structure of molecules using [[quantum mechanics]]. It was proposed early in the 20th century. The MOT explains the [[paramagnetic]] nature of [[Allotropes of oxygen#Dioxygen|O<sub>2</sub>]], which [[valence bond theory]] cannot explain.

In molecular orbital theory, [[electron]]s in a molecule are not assigned to individual [[chemical bond]]s between [[atom]]s, but are treated as moving under the influence of the [[Atomic nucleus|atomic nuclei]] in the whole molecule.<ref>{{cite book |author=Daintith, J. |title=Oxford Dictionary of Chemistry |location=New York |publisher=Oxford University Press |year=2004 |isbn=978-0-19-860918-6}}</ref> Quantum mechanics describes the spatial and energetic properties of electrons as molecular orbitals that surround two or more atoms in a molecule and contain [[valence electron]]s between atoms.

Molecular orbital theory revolutionized the study of chemical bonding by approximating the states of bonded electrons – the molecular orbitals – as [[linear combination of atomic orbitals|linear combinations of atomic orbitals]] (LCAO). These approximations are made by applying the [[density functional theory]] (DFT) or [[Hartree–Fock method|Hartree–Fock]] (HF) models to the [[Schrödinger equation]].

Molecular orbital theory and [[valence bond theory]] are the foundational theories of [[quantum chemistry]].